Partitioning - add multi-level partitioning example

Author: kmoppel

07_4_table_partitioning_multi_level.sql

@@ -0,0 +1,56 @@
+\c pg_features_demo
+
+/*
+
+As already mentioned, one can also mix different partitioning methods or even use the same method given different columns,
+but mostly only 2 different methods are combined with LIST + RANGE or HASH + RANGE being usually the most useful ones -
+for example "client" + time, meaning for each client or customer we keep action history of some months and then drop the
+old sub-partitions. Below a sample from monitoring domain, borrowed from our pgwatch2 monitoring tool, with the differenece
+that there actually the sub-partitions are managed automatically by the metric collector daemon and not created per hand.
+
+FYI - with older Postgres versions it was not really recommended to "overdo" witch such more complex multi-level approaches,
+but as of v12 one can have many levels together with thousands of sub-partitions given SQL access specifies also all these
+conditions.
+
+*/
+
+-- LIST + RANGE sample
+
+-- when lots of sub-partitions can be forseen then it's a good idea to move them into a separate schema
+CREATE SCHEMA subpartitions AUTHORIZATION demorole;
+
+SET ROLE TO demorole;
+
+-- used to "instantiate" separate metric definitions
+CREATE TABLE metrics_template (
+    time timestamptz NOT NULL DEFAULT now(),
+    dbname text NOT NULL,
+    data jsonb NOT NULL,
+    tag_data jsonb,  -- indexed "columns"
+    CHECK (false)
+);
+
+CREATE INDEX ON metrics_template USING brin (time);
+CREATE INDEX ON metrics_template USING gin (tag_data, time) WHERE tag_data NOTNULL;
+
+/*
+Something like below will be done by the pgwatch2 gatherer automatically when user activates some metric 'mymetric' for
+a monitored database named 'mydbname'
+*/
+
+CREATE TABLE "mymetric"
+  (LIKE metrics_template)
+  PARTITION BY LIST (dbname);
+
+CREATE TABLE subpartitions."mymetric_mydbname"
+  PARTITION OF "mymetric"
+  FOR VALUES IN ('mydbname') PARTITION BY RANGE (time);
+
+CREATE TABLE subpartitions."mymetric_mydbname_y2020w01"
+  PARTITION OF subpartitions."mymetric_mydbname"
+  FOR VALUES FROM ('2020-01-01') TO ('2020-01-07');
+
+INSERT INTO mymetric
+    SELECT '2020-01-01', 'mydbname', '{"numbackends": 10}';
+
+SELECT * FROM mymetric;